Mesosiderite: The Rare Stony-Iron Meteorites
In the vast diversity of space debris that reaches Earth, mesosiderites stand out as a rare and fascinating class of stony-iron meteorites. Unlike common stony meteorites or pure iron ones, mesosiderites are a hybrid, consisting of roughly equal parts metallic nickel-iron and silicate minerals. These celestial objects provide scientists with a unique window into the complex geological processes of the early solar system.
What is a Mesosiderite?
A mesosiderite is characterized as a breccia—a rock composed of broken fragments of minerals or older rocks cemented together. This results in an irregular texture where silicates and metals appear as lumps, pebbles, or fine-grained intergrowths. The silicate portion is particularly interesting to researchers, as its composition of olivine, pyroxenes, and calcium-rich feldspar closely resembles that of eucrites and diogenites.
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Composition and Classification
The makeup of a mesosiderite is a complex blend of metallic and non-metallic materials. The metallic component consists of meteoric iron, specifically the alloys kamacite, taenite, and tetrataenite. The non-metallic portion is primarily composed of silicates, such as pyroxene and calcium-rich plagioclase, along with sulphides, most notably troilite.
Scientists categorize these meteorites into several subgroups to better understand their origins:
- Subgroup A
- Subgroup B
- Subgroup C
- Anomalous types
Notable Specimens and Observed Falls
Mesosiderites are exceptionally rare. As of November 2014, only 208 specimens were known worldwide, with 56 of those recovered from Antarctica. Even more rare are observed falls—instances where the meteorite was seen hitting the Earth. Only seven such events have been recorded.
The Vaca Muerta Meteorite
One of the most significant finds occurred at Vaca Muerta in Chile's Atacama Desert. A large strewnfield yielded fragments totaling 3.8 tons. Interestingly, 19th-century ore prospectors initially mistook the shiny metal inclusions for silver. It was only after a chemical analysis revealed the presence of nickel-iron that the material was correctly identified as a meteorite.
Recorded Meteorite Falls
Several documented falls have provided precious data on these objects:
- Dong Ujimqin Qi, China (1995): Three large pieces totaling 129 kilograms.
- Estherville, USA (1879): A brilliant fireball followed by a shower of fragments totaling 320 kilograms.
- Lowicz, Poland (1935): Over 50 fragments totaling 59 kilograms.
- Other falls: Barea, Spain (1842); Varamin, Iran (1880); Dyarrl Island, Papua New Guinea (1933); and Patwar, India (1935).
Additionally, the legendary Chinguetti meteorite is believed to be a mesosiderite.
Origin and Parent Bodies
Determining where mesosiderites originate is a subject of ongoing scientific debate. The asteroid 16 Psyche has been proposed as a candidate for the parent body. However, this theory lacks a reliable delivery mechanism to explain how the material reached Earth. Current spectral analysis suggests that mesosiderites more likely derive from the Maria family of asteroids.
Key Facts
- Composition: Roughly equal parts metallic nickel-iron and silicate.
- Rarity: Only 208 known specimens as of November 2014.
- Texture: Brecciated, featuring irregular lumps of metal and silicate.
- Largest Find: Vaca Muerta (Chile) with a total mass of 3.8 tons.
- Likely Origin: The Maria family of asteroids.
| Feature | Details |
|---|---|
| Classification | Stony-iron meteorite (Breccia) |
| Metallic Components | Kamacite, Taenite, Tetrataenite |
| Silicate Components | Pyroxene, Ca-rich plagioclase, Olivine |
| Sulphide Component | Troilite |
| Known Specimens | 208 (as of Nov 2014) |
| Observed Falls | 7 |
Frequently Asked Questions
What makes a mesosiderite different from other meteorites?
Unlike stony meteorites (mostly silicate) or iron meteorites (mostly metal), mesosiderites are a balanced mix of both, structured as a breccia with an irregular, fragmented texture.
Why were the Vaca Muerta fragments mistaken for silver?
The fragments contained shiny metallic inclusions of nickel-iron, which led 19th-century prospectors to believe they had discovered a silver ore deposit.
How many mesosiderites have been found in Antarctica?
Out of the 208 known specimens recorded as of November 2014, 56 were discovered in Antarctica.
Which asteroid is the most likely source of mesosiderites?
While 16 Psyche was once a candidate, spectral analysis currently indicates that they originate from the Maria family of asteroids.
What are the primary minerals found in the silicate part of a mesosiderite?
The silicate portion primarily contains pyroxenes, olivine, and calcium-rich feldspar, making it compositionally similar to eucrites and diogenites.